IPM motor control has voltage limitations ranging from medium to high speeds. A specific direct current (dc) bus voltage level determines a series of best operating trajectories for a batch of rotor speeds. IPM characterization is normally performed only at the nominal dc bus voltage level. In other words, motor operating points, which generate direct and quadrature (d-q) current commands from a controller lookup table, are calibrated only at the nominal dc bus voltage level for a batch of rotor speeds.
In real IPM machine applications, an operating dc bus voltage may fluctuate significantly, cycling through motoring and braking modes, especially with battery applications. The fluctuating operating dc bus voltage may impact current regulation at lower dc bus voltages.